Radioactivity survey apparatus



INVENTOR SAMUEL M. ZEIL'LERS ATTOF'QNEY "Nov. 25, 1952 s. M. ZOLLERSRADIOACTIVITY SURVEY APPARATUS Filed 001: 4, 1950 Patented Nov. 25, 19522,619,601 RADIOACTIVITY SURVEY APPARATUS Samuel M. Zollers, Haddonfield,N. J., assignor, by mesne assignments, to the United States of Americaas represented by the United States Atomic Energy Commission ApplicationOctober 4, 1950, Serial No.'188,'3,3" 7

7 Claims.

This invention relates to improvements in radioactivity surveyapparatus, and particularly to an improved apparatus for measuring andindicating the. relative radioactivity of a specific radioactive source.While not limited thereto, the invention finds particular application inand willbe described with special reference to a system for indicatingthe relative radioactive contamination of a person or subject afterexposure toradioactlve materials.

the handling of radioactive material, accidental contact with thematerial frequently occurs without the knowledge of the subject handlingthe material. Therefore, it is customary to make a periodic survey ofpersonnel handling such material to detect dangerous concentrationsbefore any personal injury occurs.

Various systems have been devised for the purpose of detecting thepresence and relative concentration of radioactive materials. Theinformation obtained with such systems usually i in terms of counts,produced by radiation detecting devices, such as Geiger-Muller tubes andthe like. Since the radiation detectors commonly used also respond toambient or background radiation, such as from cosmic rays or raysgenerated by radioactive operations in the Vicinity, the count obtainedwhen a subject is examined actually is the sum of the counts from thesubject being examined and from the background. While shielding of thedetector will serve to reduce the background count to some extent, as apractical matter it is difficult if not impossible to completelyeliminate these extraneous counts. Accordingly, evaluation of theinformation obtained during a subject survey requires knowledge ofthebackground count and total count.

It is a general object of the present invention to provide an improvedapparatus for making radioactivity surveys in the presence of backgroundradiation.

A more specific object of the invention is to provide a radiation surveyapparatus in which background radiation information is automaticallyaccounted for in determining relative subject contamination.

A further object of the invention is to provide an improved radioactivecontamination monitor which will give an arbitrary and readilyunderstood indication of the relative contamination of u ie U v Inaccordance with the inyention, the foregoing and-,jot ie rel ted obzle's a d a v ages are attainedby embodying in a radioactivity surveyapparatus a system of comparison relay-actuated 2 switches in whichbackground radiation information is stored for comparison withinformation obtained by surveying a subject in the presence ofbackground radiation.

A more completeunderstanding of the 'inven tion can be had from thefollowing description of an illustrative embodiment thereof, whenconsidered in connection with the accompanying drawing, the singlefigure of which isa partially schematic and partially block diagram ofan apparatu embodying the principles of the invention.

Referring to the drawing, the apparatus shown comprises a system fordetermining the number of radioactive emanations coming from a subjectunder survey during a predetermined time interval. In brief, operationof the apparatus includes initial calibration operation during whichinformation is obtained and stored as to the ambient or backgroundradioactivity in the area of the apparatus, followed by a subject surveyperiod during which the contamination of the subject being surveyed iscomputed and indicated in terms of its relation to the previouslyobtained background information.

The apparatus shown has two principal sections. The first is thedetecting and counting section, wherein radioactive emanations aredetected and converted to a form suitable for use in the selecting andindicating section.

The detecting and counting section of the system is conventional, andhas been shown in block diagram form. A Geiger-Muller tube Ill, orequivalent, is provided for generating an electrical pulse each time aray passes through the tube I I]. The tube ii] i connected to a scalingcircuit I2, such as a set of binary counter networks or the like, toscale, down the output pulses of the tube H]. For example, the scalingcircuit l2 may produce one output pulse for each eight pulses generatedin the tube In. The scaling circuit I2 is connected to supply pulsesthrough a power amplifier It to the operatingwinding I 6 of a relay l 8.This relay I 8 has a movable contact 20 which engages a fixed contact 22each time apulse is delivered from the scaling circuit [2. As will beexplained shortly, closing of the relay contacts 20, 22 causes a voltagepulse to be delivered to the selecting and indicating sections of theapparatus. i I V For simplicity, a single power supply system 24 isshown for converting alternating voltagjs'jto unidirectional voltage forthe detector circuits l 0-I4 and for certain of the relays referredtohereinafter. The power supply 24 is to be energized by alternatingvoltage from a suitable source (not shown) through a main switch 21.

While the detecting and counting circuits IIII4 will operatecontinuously once the main power switch 21 is closed, it will beunderstood that the relative concentration of radioactive material in anarea can be determined by a relatively brief survey of the area. Thatis, the area of interest can be surveyed for a predetermined time, andthe relative radioactivity thereof expressed in terms of counts persecond, counts per minute, or the like. a

As was previously stated, when a radioactivity survey is made of aspecific source, such as a possibly contaminated area on a human body,an allowance must be made for background radiation in the vicinity ofthe apparatus.

In the remaining portions of the apparatus shown, provision is made forobtaining background radiation information during a preselected thesubject during an equal tim interval, and

automatically comparing the subject and background information.

Considering, first, the background information storage system, it willbe seen that the fixed contact 22 of the counter output relay I8 isconnected to the movable contact 26 of a single pole double throw switch28. This switch 28, designated the background-subject switch, has a pairof fixed contacts 30, 32 which are connected to the operating windings84, 36 of a pair of stepping relays 38, 40, designated the backgroundcount and subject count relays, respectively. The relays 38, 48 are ofthe type wherein movable contacts are adapted to be moved consecutivelyover a plurality of fixed contacts, step by step, moving one stepforward in response to each impulse of current through the relaywinding. Since such relays are well known in the art, a further detaileddescription thereof is believed to be unnecessary.

The background count relay 38 is provided with three separate banks ordecks of contacts 42, 44, 46 each deck having its individual movablecon- .tact 48, 58, 52. All of the contacts 48, 58, 52 are mechanicallyconnected to move forward in synchronism in response to energization ofthe relay winding 34. For simplicity, only enough of the lower contact38, and that the movable contact 20 of the counter output relay I8 isconnected to the voltage source +R, then each time a pulse is receivedby the counter output relay l8, each of'the movable contacts 48, 59, 52will be advanced one step on its associated deck of fixed contacts. Ifthe movable contacts 48, 5B, 52 all were in the zero position to beginwith, then the final position of these contacts would be indicative ofthe number of pulses received by the output relay I8.

In order to insure that the movable contacts 48, 50, 52 all Will be inthe zero or home position prior to taking a background count, themovable contact 54 of a switch 56 is connected to be moved downwardlyinto contact with a fixed contact 58 when the background-subject switch28 is moved to the background position. This operation completes acircuit from the voltage source 24 through the switch contacts 54, 58,through make-beforebreak contacts 60, 6| on a relay 62, to the movable(upper deck) contact 48 of the background relay 38. All of the fixedcontacts 08,-58. of the upper deck 42, expect the first or Be positioncontact, are connected to an auxiliary fixed contact 68 on thebackground relay 38. This fixed contact 66 normally engages a movablecontact 68. Therefore, if the movable upper deck contact 48 is in anyposition other than the zero position when the background homing switch56 is closed, voltage will be applied to the background relay winding34. All of the background relay contacts 48, 5B, 52 will step forwardone position, and the auxiliary contacts 86, 58 will open, breaking thecircuit to th winding 34. The auxiliary contacts 66, 68 then will closeagain, and the action just described will be repeated until all of themovable contacts 48, 58, 52 reach the zero position. When this occurs,voltage will be applied from theme contact on the upper contact deck 42to the winding 84 of the homing control relay 62. When the homingcontrol relay 62 isenergized, a movable contact 68 will move up to openthe circuit through the make-before-break contacts 68, BI, and tocomplete a holding circuit to the winding 64 of the homing controlrelay. .Thus, once the background relay 38 is in the home position,homing action cannot take place without first deenergizing the homingcontrol relay 64 by opening the homing switch 56.

The homing control relay 62 also is provided with a set of contacts I8,I2 which close when th relay 62 is energized. These contacts close acircuit which provides for time-controlled background counting, as willnow be described.

Timing of counting operations is provided by a timer motor I4 whichoperates under the control of three relays I8, 88, 82, a clutchmechanism 84, and a snap-switch I6. The clutch 84 is controlled by asolenoid 86, and operates (when the solenoid 86 is energized) to couplethe motor I4 to an arm 88 for actuating the switch I6. That is, with thsolenoid 86 and the motor I4 energized, the arm 88 gradually will movein a clockwise direction until it engages the movable contact 98 of theswitch IS. The movable contact 98 then will snap out of engagement withthe contact 52 and into engagement with the other fixed contact 94-.When the main power switch 21 is closed, to turn the apparatus on,voltage will be applied to a movabl contact 95 on the first timercontrol relay I8. As long as the relay I8 is deenergized, voltage Willbe applied to energize the solenoid 85 through the movable contact 96and a fixed'contact 98 on the relay I8.

At the same time, the motor I4 will receive energizing voltag throughthe contacts 98, 92 of the timer switch I5. The timer motor will beginoperating and eventually will actuate the switch This will open themotor circuit, and will supply operating voltage to the winding I of arelay I82 through the contacts 98, 54. However, even though the motorcircuit is open, the timer switch I6 will be held in actuated position,energizing the winding I08, as long as the solenoid 88 keeps the clutch84 engaged.

It will be noted that the movable contact 20 of the counter output relayI8 is connected to a fixed contact I04 on the relay I82. As long as therelay I02 is deenergized, the contact I04 will be engaged by a movablecontact I06 which is connected to the voltage source 24. However, thecircuit from the voltage source 24 to the movable contact 20 of thecounter output relay I8 will be open whenever the counter output controlrelay I02 is energized.

To start a counting interval, the solenoid 88 aemgemailbwcther.timer:switch: .16. to :return :tostarting position;IniigeneraL: the'circu'it for the solenoid Bi isz: deenerlgized by'energizing the first timer control reIay'"'I8. This; relay 'IBJcan beenergized byicompleting' 'axcircuit from the winding I08thereofatl'irough' make-before-break contacts I I0,HZEOfiYthQjhild,1131111811.COIltI'OI relay, 82 to the mai'npower switch-2Teither through a switch I I3 orjthroughlcontacts-10;. 12 on thebackground homing ;control.relay :62. In backgroundcountingsfoiftexample, the homing relay 82 is. energizedass-previouslydescribed, closing the contacts III, 1.2. This energizesthe timer control relay I8, assjust described, deenergizing the solenoid.86. In turn, the timer switch will snap over to closeits:contacts1:9Il-, .92. This will energize: both; the timermotor-lltand the second timer control re- 12.522805.

Wh'en'the: secondtimer. control re'lay 80 is energ'i'zed', a: circuitwill be completed through contacts I I4, IIIS thereof andthroughcontacts I Iii, I of previously energized'relay I3 forenergizingthethird timer control relay 82. When this relay 821senergized, make-before-break contacts H0, vI I2 thereof open; byactionof movable contact- I I5, deenergizing the first timer controlrelayflB-and, hence, energizing the solenoid 85. At the same. time, aholding circuit'for' this relay 82- willi-be'completedthrough contactsH2, H5

thereof. Since the timer motor 14 also will be energized at" this time,atiming cycle will begin duringwhich background radiation informationcanbe received and stored at the background counting relay 38; Theduration of the counting'interval will be a function of the operatingspeed of 'the'motor I4 and the distance of travel ofthe actuatingarm-"88; During this interval, counts actuating the counter output relayI8 will be passed on to the background relay 38. The timing intervalwill end when the timer switch 16 operates to deenergize the motor I4and energize the relay I02. The position of the various movable contacts48, 50, 52 on-the background counting relay- 38 now will represent theamount of"radi'at'ion. detected by the Geiger-Muller tube I'G during.the background. counting interval.

Withbackground count information stored. as justldes'cribed, theapparatusnow will be ready for subject" survey.

As a firstlste'p, the background-subject switch 28 is" changed 'to openthe circuit through contacts 26; 30 and'close the circuit throughcontacts 26, 32. This operation will deenergize the homing controlrelay62, thereby opening the contacts 10, 'lzithereofan'd removing theby-pas's around the switch H3. In turn, the third timer controlre1ay"82*will be deener'gize'd. However, since the solenoidtfii is "notdeen'ergized, the timer switch I6 will be held in" actuated position.

When a subject is in position to be surveyed, the-switch II3'is' closedto start "subject counting? Forexample, the-switch I It may beautomatically actuated when the subject is in position in front of thedetector-I9.

When the switch H3 closes, a timed counting sequence occurs as wasalready described in connection with the closing of contacts III, I2 onthe background-homing relay $2. This time, of course, operation of thecounter output relay I8 applies pulses to the operating winding 36'ofthe subject. relay dihcausing the movable contacts I22, I24thereof'tomove forward one step for each'p'ulsereceived. Aswillbeexplained hereinafter; the contacts I22,- I25 will be-in the-zeropositiomat the beginningof each" subject count mg; interval,- so that:the'position of the contacts I22; I24 at "the endof such" intervalalways-will represent accuratelythe total. radiation intercepted by;the: detector I I] duringthat interval;

Aswaspreviously stated; the present inventionprovides means to:determine the radioactivity of a subject relative tobackground-radiation in the area. That is,. counts obtainedduring'afsubject counting interval. will be the sum of the backgroundradiation and radiation com.- ing fromthe subject. Therefore, thissubject count amustbecomparedwith the background count to determine theactual amount-of. radiation coming from the subject. 7

In the illustrative embodiment oftheinven. tion; shown in. the drawing,three -=ind-icators zare providedand arranged to indicatethree possibleconditionsof asubject. Oneof. the indicators I26-may comprise. a greenlight, asecondindicator I28. may comprise a yellow. light, and a thirdindicator I30 may comprise a red light.

It is contemplated that the appearanceof a green light at the end of asubject counting-interval will indicate that the subject is notcontaminated, that the appearance of ayellowlight will indicate probablecontamination, and that the appearanceof a red light willindicatedefinite contamination. Each ofthese categories will be representative.of some predetermined ratio between background. plus subjectcount andback-- ground count.

It will, ofc'ourse, be understood that difierent types of radioactivematerial willhave different potentially harmful efiects, so that if thecontamination of the subject is, say, three times. as great as the.normal background count in the area,v it might be adangerous conditionforone radioactive. material although not for another. In the presentexample, it is assumed that a contamination equal to twice thebackground count is sufficiently dangerous. to Warrant a probablycontaminated indication, and that a contamination five times backgroundcount is sufficiently dangerous to warrant an indication of definitelycontaminated. However, it will be seen that the subject relay 49 has twocontact decks I32, I34. The upper deck I 32 is provided to insure homingaction, as will be described hereinafter. The

lower deck I34 cooperates with the middle and lower decks 44, 460i thebackground counting relay to control actuation of the indicators I26--The indicators I25I3I3 are under the immediate controlof a pair ofrelays I36, I38. The winding Mt of one relay I36 is connected to themovable contact 52 on the lower deck 46 of the backgroundcountingrelaytii. The winding I42 of the other indicator control relayI38 is connected to the movable contact 5% on the middle'deck. M-of thebackground relay 38. Oneor both of the'relays I36;- Iiit may beenergized, depending on the relative positions of the movablecontaots'tii; 5-2 and 24 on the stepping re'lays 38 49.

It'will be noted'that connections aremadebetween certain of the fixedcontacts on the middle and. lower decks of the background relay 38 andthe lower deck I34 of the subject relay 40'. Specifically, in thepresent example, connections are; made from contacts Ic, 20, 3c, 4c onthe lowerdeck 46 of. the background relay 38 to contacts 2's, 4d, 6a,.8aon the lower-deck I34 of the subjectrelay M.- This representsta ratio oftwo to. onebetween the contact numbers; Con-,-

nections: also arecziiade fr'dmz. contacts:- Ia, 2s,-

7 3b on the middle deck 44 of the background relay 38 to contacts 51, Weand Ia on the lower deck of the subject relay 46. This provides a ratioof five to one between the contact members.

The movable contact I24 of the subject lower deck I34 is connected to amovable contact I44 on the counter control relay I62. A cooperatingfixed contact I46 isconnected to the fixed contact 62 on the timerswitch 16. Therefore, whenever the timer switch 16 is in position tocomplete a circuit through the contacts 96, 62 thereof, the subjectrelay lower deck contact I24 will receive voltage from the switch 21. Asthis contact I24 is moved forward in sequence over the associated fixedcontacts Is, 2s, etc., voltage from the switch 21 will appear, in turn,at each of the background lower deck contacts Ic, 2c, etc. If thesubject contact I24 moves far enough, voltage also will appear, in turn,at each of the background middle deck contacts Ib, 0,

etc.

Prior to subject survey, the indicator control relays will bedeenergized, and the green indicator I26 will be energized through theswitch 21 and through a pair of contacts I56, I58 on the relay I36.

Assume that the background count in a given case was equal to three,leaving the movable contacts 56 and 52 of the background relay 38 onassociated contacts 3b and 3c, respectively. Assume also that a givensubject, when surveyed, produced a count of seven, thereby moving themovable contact I24 to contact 16. on the associated deck I34. Duringsubject survey period, the first efifect on the indicator system willoccur when the movable contact I24 engages the fixed contact Be. At thistime, voltage will be applied through the connecting link to contact 30on the background lower deck 46, thereby energizing the relay I 36. Assoon as the relay I36 is energized, a holding circuit will beestablished for the relay I36 from the voltage source through a pair ofcontacts I52, I54 on the first timer control relay 18 and through a pairof contacts I48, I56. Therefore, although the movable contact I24 willcontinue on to its next fixed contact 1d, the relay I36 will remainenergized. En-

ergization of the relay I 36 also will open the circuit through thecontacts I56, I58 and will complete a circuit to the yellow indicatorI28 through contacts I56, I66 on the relay I36 and through contacts I62,I64 on the relay I36. Therefore, when the subject count is completed inthe example given, the yellow indicator I28 would be energized,indicating that the ratio between subject plus background and backgroundcounts is at least two to one, but less than five to one.

If the subject count had been fifteen in the foregoing example, thesequence just described would occur, with these additional steps. As themovable background contact I24 reached its associated fixed contact I5d, a circuit would be completed through the background relay middledeck contacts 3b and 56 to the winding I42 of the relay I38. This wouldenergize the relay I33, completing a holding circuit through contactsI66, I68 thereof. Also, the circuit through the contacts I62, I64 to theyellow indicator I28 would open, and a circuit would be completed to thered indicator I36 through contacts I62, I16 on the relay I38. Of course,if the subject count had been higher than fifteen, the holding circuitfor the relay I38 would have insured continued energization of the redindicator I36.

After a subject has been surveyed, the switch H3 is opened (preferably,automatically, as the subject moves out of survey position). This willdeenergize the third timer control relay 82, establishing a homingcircuit for the subject count relay 46 through a pair of, contacts I12,I14 on the timer control relay 82. This circuit extends from the voltagesource 24 through contacts I66, I61 on the counter output control relayI62 and through the contacts I12, I14 to the movable upper deck contactI22 of thesubject count relay 46. The homing action of the subject countrelay 46 will be similar to that previously described for the backgroundrelay 38, leaving both movable contacts I22, I24 in the zero position.

When the switch I I3 is closed for the next sub ject survey, thetemporary energization of the first timer control relay 18 wil1 open theholding circuits of the indicator control relays I36, I38, therebypreparing the indicators I26, I28, I36 for proper operation.

It can be seen that the present invention provides 'a convenient surveysystem especially adapted for use in rapidly surveying a large number ofuntrained personnel, since it is unnecessary for the subject to make anycalculations or consider any numerical ratios. The fixed contact decks44, 46, I26 can be equipped with so-called pin jack connections, makingit a simple matter to change the count ratios whenever necessary. Oncethe background count has been determined, the apparatus can be operatedwithout supervision until change in conditions make it necessary torecalibrate. Fail-safe circuits can readily be incorporated, if desired,so that a failure of power at any point will immediately be manifestedby a total lack of count indications.

Since many changes could be made in the specific apparatus shown anddescribed, all within the scope and spirit of the invention, theforegoing is to be construed as illustrative, and not in a limitingsense.

1. A radioactivity survey apparatus compris ing a radiation detector,first and second relays each having an operatin winding and a set offixed contacts, a movable contact for each, said fixed contact set andadapted to be moved sequentially from one to another of the associatedfixed contacts in response to energization of the associated relaywinding, means selectively to energize either of said operating windingsin response to detection of a predetermined number of rays by saiddetector, means connecting prevselected ones of said fixed contacts inone set to preselected ones of said fixed contacts in the other set, anindicator, and means connected to actuate said indicator in response tomovement of said movable contacts to connected ones of said fixedcontacts.

2. A radioactivity survey apparatus comprising a radiation detector,first and second relays each having an operating winding, said firstrelay having at least one set of fixed contacts and said second relayhaving at least two sets of fixed contacts, a movable'contact for eachsaid fixed contact set and adapted to be moved sequentially from one toanother of the associated fixed contacts in response to energization ofthe associated relay winding, means selectively to energize eitherofsaid. operating winding-s in response to detection of a predeterminednumber of rays by said detector, means connectin preselected ones ofsaid fixed contacts in'said one set to preselected ones of said fixedcontacts in connected to actuate one of said indicators in response tomovement of said movable contacts to connected ones of said fixedcontacts in two of said sets and to actuate another of said indicatorsin response to movement of said movable contacts to connected ones ofsaid fixed contacts in a difierent two of said sets.

3. In a radioactivity survey apparatus, in combination, a radiationdetector, first and second sets of fixed contacts, a movable contactassociated with each said set, m'eans selectively to move either of saidmovable contacts sequentially from one to another of the fixed contactsin the set associated therewith in reponse to detection of apredetermined number of rays by said detector, connections frompreselected ones of the fixed contacts in one of said sets topreselected ones of the fixed contacts in the other of said sets, anindicator, means to actuate said indicator, and means connected to saidmovable contacts and responsive to movement of said movable contacts toconnected ones of said fixed contacts for operating said actuatingmeans.

4. A radioactivity survey apparatus comprising a radiation detector,first and second relays each having an operating winding, each saidrelay having a set of multiple fixed contacts, a movable contact foreach said fixed contact set and adapted. to be moved sequentially fromone to another of its associated fixed contacts in response toenergization of its associated relay winding, a third relay having anoperating winding and having a pair of contacts adapted to be closedupon energization of said last-named winding, means connecting said lastnamed winding to said detector for energization of said last namedwinding in response to detection of a predetermined number of rays bysaid detector, means to energize either said first or said second relaywinding in response to closing of said pair of contacts, connectionsfrom preselected ones of the fixed contacts in one of said contact setsto preselected ones of said fixed contacts in the other of said sets, anindicator, and means to actuate said indicator in response to movementof said movable contacts to connected ones of said fixed contacts insets.

5. A radioactivity survey apparatus comprising a radiation detector,first and second relays each having an operating winding, said firstrelay having at least one set of multiple fixed contacts and said secondrelay having at least two sets of multiple fixed contacts, a movablecontact for each said fixed contact set and adapted to be movedsequentially from one to another of its associated fixed contacts inresponse to energization of its associated relay winding, meansconnected to said detector to selectively energize either said first orsaid second relay winding in response to detection of a predeterminednumber of rays by said detector, connections from preselected ones ofthe fixed contacts in both said two sets, a plurality of indicators,means to actuate one of said indicators in response to movement of saidmovable contacts to connected ones of said fixed contacts in one pair ofsaid sets, and means to actuate another of said in- I said two sets, aplurality of indicators, and means dicators in response to movement ofsaid movable contacts to connected ones of said fixed contacts inanother pair of said sets.

6. A radioactivity survey apparatus comprising a radiation detector,first and second relays each having an operating winding, each saidrelay having a set of multiple fixed contacts, a movable contact foreach said fixed contact set and adapted to be moved sequentially fromone to another of its associated fixed contacts in response toenergization of its associated relay windings, a circuit for selectivelyenergizing either said first or said second relay winding in response todetection of a predetermined number of rays by said detector, means toclose said energizing circuit for preselected time intervals,connections from preselected ones of the fixed contacts in one of saidcontact sets to preselected ones of said fixed contacts in the other ofsaid sets, an indicator, and means to actuate said in dicator inresponse to movement of said movable contacts to connected ones of saidfixed contacts.

7. A radioactivity survey apparatus comprising a radiation detector,first and second relays each having an operating winding, said firstrelay havin'g at least one set of multiple fixed contacts and saidsecond relay having at least two sets of multiple fixed contacts, amovable contact for each said fixed contact set and adapted to be movedsequentially from one to another of its associated fixed contacts inresponse to energization of its associated relay winding, a third relayhaving an operating winding connected to said detector and having a pairof contacts adapted to be closed upon energization of said last-namedwinding, a selector switch, a circuit for energizing either said firstor said second relay winding and including said pair of contacts andsaid selector switch, means to close said energizing circuit forpreselected time intervals, connections from preselected ones of thefixed contacts in one of said contact sets to preselected ones of saidfixed contacts in both said two sets, a plurality of indicators, meansto actuate one of said indicators in response to movement of saidmovable contacts to connected ones of said fixed contacts in one pair ofsaid sets, and means to actuate another of said indicators in responseto movement of said movable contacts to connected ones of said fixedcontacts of another pair of said sets.

SAMUEL M. ZOLLERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,019,863 Kolm Nov. 5, 19352,532,503 Kennedy et a1. Dec. 5', 1950 OTHER REFERENCES A Direct-ReadingRate Ratio Meter, Evans et al. Rev. of Sci. Instruments, Nov. 1939, vol.10, pages 339, 344.

